It's a compilation of 10 mini-games, with an emphasis on decorations, clothes and jewelry.

There's also a trailer:

Help Hello Kitty and Sanrio friends prepare for their picnic in the park in this fun collection of 10 mini-games! Collect all your picnic goodies and decorate five scenes including Hello Kitty's bedroom, kitchen, and more. Earn apple rewards to unlock special decorations, outfits, and jewelry to customize looks for Hello Kitty in a bonus scene!

Holidays! - Play Hello Kitty Picnic on holidays like New Year's Day, Valentine's Day, Independence Day, Halloween and more. Receive special items such as shirts, hats, accessories, and stickers for decorating scenes and dressing Hello Kitty in the special "Dressing Up" scene!